NetBSD Problem Report #42367

From bharder@methodlogic.net  Mon Nov 23 20:10:29 2009
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Date: Mon, 23 Nov 2009 12:10:20 -0800
From: bharder <bharder@methodlogic.net>
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To: gnats-bugs@gnats.NetBSD.org
Subject: MTU adjustments causing wm(4) to drop carrier
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>Number:         42367
>Category:       kern
>Synopsis:       wm(4) interface dropping carrier when MTU too low (?)
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    msaitoh
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Nov 23 20:15:00 +0000 2009
>Closed-Date:    Tue Dec 17 21:29:15 +0000 2019
>Last-Modified:  Tue Dec 17 21:29:15 +0000 2019
>Originator:     bharder <bharder@methodlogic.net>
>Release:        NetBSD 5.0_STABLE
>Organization:
	Method Logic Digital (http://www.methodlogic.net)
>Environment:
System: NetBSD oxford 5.0_STABLE NetBSD 5.0_STABLE (oxford) #10: Mon Nov 23 00:44:49 PST 2009 root@oxford:/usr/obj/sys/arch/i386/compile/oxford i386
Architecture: i386
Machine: i386
>Description:
	Noticed with latest dhcpcd update to 5.1.3, specifically "Default to requesting an MTU" behaviour.
	Excerpt from /var/log/messages (with IP addresses obfuscated):

	Nov 23 00:10:48 oxford dhcpcd: wm0: leased 123.45.67.89 for 3600 seconds
	Nov 23 00:10:49 oxford dhcpcd: wm0: MTU set to 576
	Nov 23 00:10:49 oxford dhcpcd: forking to background
	Nov 23 00:10:49 oxford dhcpcd: wm0: carrier lost
	Nov 23 00:10:49 oxford dhcpcd: wm0: MTU restored to 1500
	Nov 23 00:10:51 oxford dhcpcd: wm0: carrier acquired
	Nov 23 00:10:51 oxford dhcpcd: wm0: rebinding lease of 123.45.67.89
	Nov 23 00:10:51 oxford dhcpcd: wm0: acknowledged 123.45.67.89 from 98.76.54.32
	Nov 23 00:10:51 oxford dhcpcd: wm0: checking for 123.45.67.89
	Nov 23 00:10:56 oxford dhcpcd: wm0: leased 123.45.67.89 for 3593 seconds
	Nov 23 00:10:56 oxford dhcpcd: wm0: MTU set to 576
	Nov 23 00:10:56 oxford dhcpcd: wm0: carrier lost
	Nov 23 00:10:56 oxford dhcpcd: wm0: MTU restored to 1500
	Nov 23 00:10:58 oxford dhcpcd: wm0: carrier acquired
	Nov 23 00:10:58 oxford dhcpcd: wm0: rebinding lease of 123.45.67.89
	Nov 23 00:10:58 oxford dhcpcd: wm0: acknowledged 123.45.67.89 from 98.76.54.32
	Nov 23 00:10:58 oxford dhcpcd: wm0: checking for 123.45.67.89
	Nov 23 00:11:02 oxford dhcpcd: wm0: leased 123.45.67.89 for 3586 seconds
	Nov 23 00:11:03 oxford dhcpcd: wm0: MTU set to 576
	Nov 23 00:11:03 oxford dhcpcd: wm0: carrier lost

>How-To-Repeat:
	If I understand correctly, if the dhcp server is sending
	sufficiently small MTU, and dhcp client is honouring it,
	this behaviour is triggered in wm(4).
>Fix:
	Yes, please. My understanding of this problem was aided by
	discussion w/ Roy Marples in irc on #netbsd. He may be able
	to provide more details. Thanks, Roy.

>Release-Note:

>Audit-Trail:

Responsible-Changed-From-To: kern-bug-people->mine
Responsible-Changed-By: msaitoh@NetBSD.org
Responsible-Changed-When: Sat, 23 Jan 2010 13:08:31 +0000
Responsible-Changed-Why:
mine


Responsible-Changed-From-To: mine->msaitoh
Responsible-Changed-By: msaitoh@NetBSD.org
Responsible-Changed-When: Sat, 23 Jan 2010 13:09:03 +0000
Responsible-Changed-Why:
oops


State-Changed-From-To: open->closed
State-Changed-By: roy@NetBSD.org
State-Changed-When: Tue, 17 Dec 2019 21:29:15 +0000
State-Changed-Why:
This is worked around in dhcpcd-7 by applying the MTU to the routes
rather than the interface.

bch no longer uses NetBSD-5 so he's happy for this to be closed.


>Unformatted:

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